<!doctype html>
<!--
Copyright 2018 The Immersive Web Community Group

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-->
<html>
  <head>
    <meta charset='utf-8'>
    <meta name='viewport' content='width=device-width, initial-scale=1, user-scalable=no'>
    <meta name='mobile-web-app-capable' content='yes'>
    <meta name='apple-mobile-web-app-capable' content='yes'>

    <!-- Origin Trial Token, feature = WebXR Device API, origin = https://immersive-web.github.io, expires = 2018-08-28 -->
<meta http-equiv="origin-trial" data-feature="WebXR Device API" data-expires="2018-08-28" content="AnNpu7ceXvLew05ccD8Zr1OZsdZiB2hLQKK82kTTMDwF7oRKtP3QEJ4RzkeHrmB8Sq0vSV6ZNmszpBCZ0I8p9gAAAABceyJvcmlnaW4iOiJodHRwczovL2ltbWVyc2l2ZS13ZWIuZ2l0aHViLmlvOjQ0MyIsImZlYXR1cmUiOiJXZWJYUkRldmljZSIsImV4cGlyeSI6MTUzNTQxNDQwMH0=">

    <title>Fallback Rendering</title>

    <link href='css/common.css' rel='stylesheet'></link>

    <!--The polyfill is not needed for browser that have native API support,
        but is linked by these samples for wider compatibility.-->
    <!--script src='https://cdn.jsdelivr.net/npm/webxr-polyfill@latest/build/webxr-polyfill.js'></script-->
    <script src='js/xrray-polyfill.js' type='module'></script>
    <script src='js/webxr-polyfill.js'></script>

    <script src='js/webxr-button.js'></script>
  </head>
  <body>
    <header>
      <details open>
        <summary>Fallback Rendering</summary>
        <p>
          This sample demonstrates a way to fallback to rendering the scene when
          WebXR isn't available.
          <a class="back" href="./index.html">Back</a>
        </p>
      </details>
    </header>
    <script type="module">
      import {Scene} from './js/cottontail/src/scenes/scene.js';
      import {Renderer, createWebGLContext} from './js/cottontail/src/core/renderer.js';
      import {Gltf2Node} from './js/cottontail/src/nodes/gltf2.js';
      import {QueryArgs} from './js/cottontail/src/util/query-args.js';
      import {SkyboxNode} from './js/cottontail/src/nodes/skybox.js';
      import {mat4} from './js/cottontail/src/math/gl-matrix.js';

      // If requested, initialize the WebXR polyfill
      if (QueryArgs.getBool('allowPolyfill', false)) {
        var polyfill = new WebXRPolyfill();
      }

      // XR globals.
      let xrButton = null;
      let xrImmersiveRefSpace = null;
      let xrNonImmersiveRefSpace = null;

      // WebGL scene globals.
      let gl = null;
      let renderer = null;
      let scene = new Scene();
      scene.addNode(new Gltf2Node({url: '../media/gltf/space/space.gltf'}));
      scene.addNode(new SkyboxNode({url: '../media/textures/milky-way-4k.png'}));

      let projectionMatrix = mat4.create();
      let viewMatrix = mat4.create();

      function initXR() {
        xrButton = new XRDeviceButton({
          onRequestSession: onRequestSession,
          onEndSession: onEndSession,
          supportedSessionTypes: ['immersive-vr']
        });
        document.querySelector('header').appendChild(xrButton.domElement);

        if (navigator.xr) {
          requestInlineSession()
          .then((session) => {
            gl.canvas.addEventListener('touchend', () => {
              session.end().then(() => {
                requestInlineSession({ optionalFeatures: ['local'] });
              }, { once: true });
            })
          });
        } else {
          // If navigator.xr isn't present in the browser then we need to use
          // the fallback rendering path.
          initFallback();
        }
      }

      // When we hit the fallback path, we'll need to initialize a few extra
      // variables in order to render correctly.
      function initFallback() {
        initGL();
        document.body.appendChild(gl.canvas);

        // Using a simple identity matrix for the view.
        mat4.identity(viewMatrix);

        // We need to track the canvas size in order to resize the WebGL
        // backbuffer width and height, as well as update the projection matrix
        // and adjust the viewport.
        function onResize() {
          gl.canvas.width = gl.canvas.offsetWidth * window.devicePixelRatio;
          gl.canvas.height = gl.canvas.offsetHeight * window.devicePixelRatio;
          mat4.perspective(projectionMatrix, Math.PI*0.4,
                           gl.canvas.width/gl.canvas.height,
                           0.1, 1000.0);
          gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
        }
        window.addEventListener('resize', onResize);
        onResize();

        // We'll kick off the render loop using the window's
        // requestAnimationFrame function.
        window.requestAnimationFrame(onWindowFrame);
      }

      // Since both the XR and fallback paths need to do the same WebGL
      // initialization code, we've moved that code out to it's own function.
      function initGL() {
        if (gl)
          return;

        gl = createWebGLContext({
          xrCompatible: true
        });

        renderer = new Renderer(gl);

        scene.setRenderer(renderer);
      }

      function onRequestSession() {
        navigator.xr.requestSession('immersive-vr').then((session) => {
          session.mode = 'immersive-vr';
          xrButton.setSession(session);
          onSessionStarted(session);
        });
      }

      function requestInlineSession(options) {
        return navigator.xr.requestSession('inline', options)
          .then((session) => {
            session.mode = 'inline';
            return onSessionStarted(session);
          });
      }

      function onSessionStarted(session) {
        session.addEventListener('end', onSessionEnded);

        initGL();

        session.updateRenderState({
            baseLayer: new XRWebGLLayer(session, gl)
        });

        session.requestReferenceSpace('local').then((refSpace) => {
          return refSpace;
        }, (e) => {
          if (!session.mode.startsWith('immersive')) {
            // If we're in inline mode, our underlying platform may not support
            // the stationary reference space, but an identity space is guaranteed.
            return session.requestReferenceSpace('viewer');
          } else {
            throw e;
          }
        }).then((refSpace) => {
          if (session.mode.startsWith('immersive')) {
            xrImmersiveRefSpace = refSpace;
          } else {
            xrNonImmersiveRefSpace = refSpace;
          }
          session.requestAnimationFrame(onXRFrame);
        });

        return session;
      }

      function onEndSession(session) {
        session.end();
      }

      function onSessionEnded(event) {
        if (event.session.mode.startsWith('immersive')) {
          xrButton.setSession(null);
        }
      }

      function onXRFrame(t, frame) {
        let session = frame.session;
        let refSpace = session.mode.startsWith('immersive') ?
                         xrImmersiveRefSpace :
                         xrNonImmersiveRefSpace;
        let pose = frame.getViewerPose(refSpace);

        session.requestAnimationFrame(onXRFrame);

        scene.startFrame();

        if (pose) {
          gl.bindFramebuffer(gl.FRAMEBUFFER, session.renderState.baseLayer.framebuffer);
          gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

          for (let view of pose.views) {
            let viewport = session.renderState.baseLayer.getViewport(view);
            gl.viewport(viewport.x, viewport.y,
                        viewport.width, viewport.height);

            scene.draw(view.projectionMatrix, view.transform.inverse.matrix);
          }
        }

        scene.endFrame();
      }

      // This is the bulk of the fallback rendering loop. Notice that it looks
      // a lot like a simplified version of the XR frame loop. Samples after
      // this one will do some work to hide this for code readability purposes.
      function onWindowFrame(t) {
        window.requestAnimationFrame(onWindowFrame);

        scene.startFrame();

        // We can skip setting the framebuffer and viewport every frame, because
        // it won't change from frame to frame and we're updating the viewport
        // only when we resize for efficency.
        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

        // We're drawing with our own projection and view matrix now, and we
        // don't have a list of view to loop through, but otherwise all of the
        // WebGL drawing logic is exactly the same.
        scene.draw(projectionMatrix, viewMatrix);

        scene.endFrame();
      }

      // Start the XR application.
      initXR();
    </script>
  </body>
</html>
